Ice thickness is an important question for many types of winter sports or other load-bearing tasks. For example, pond ice is not regarded as generally safe for skating until substantially clear ice has formed to about six inches thickness. Lake ice is considered safe for ice fishing when the thickness has reached about twelve inches to allow for movement of heavy loads across the ice. In the Arctic, winter roads across bodies of water are not opened until the underlying icebed has thickened to twenty or more inches.
Various apparatuses and methods have been developed for measuring ice thickness. For example, ice thickness has been measured by forming an electrical circuit with an existing ice sheet connected in series to a power supply, and then checking the resistance of the circuit, as taught by U.S. Pat. No. 4,287,472 issued to Pan. Ice thickness also has been measured by deploying two induction coils above an ice sheet, energizing one coil, and estimating the thickness of the ice sheet based on the power produced by the second coil, as taught by U.S. Pat. No. 4,418,570 issued to Warren, Jr. Ultrasonic and radar measurement devices also have been employed, for example by Clasen (US 2008/0295599). However, these electrical or non-penetrating methods have wide ranges of error—up to thirty five percent (35%) for the induction apparatuses, as reported by Pan. More simply, ice thickness has been measured by drilling a hole and lowering a ruler to the undersurface of the ice sheet, as taught by U.S. Pat. No. 4,375,721 issued to Ueda.
However, all these measurement methods require expensive and complicated electronic equipment and/or physical presence of a measuring person on the ice sheet being measured. Expensive equipment is not preferred for most winter sports or other tasks, while the physical presence of a measuring person is not desirable until after safe ice thickness already has been verified. Thus, it is desirable to provide an inexpensive device that can indicate to someone at a remote location off the ice when the ice has reached a safe thickness for winter sports or other tasks.